IDO1 and gastroenteritis: In striking contrast, single-cell transcriptomic profiling reveals that IDO1-high macrophage subsets in Crohn’s disease exhibit marked enrichment of M1-associated signature genes (including iNOS, IL-6, and TNF-α), while demonstrating strong topological association with the development of mesenteric “creeping fat”—a hallmark pathological feature of intestinal inflammation (51).